| Summary: | 碩士 === 國立臺北科技大學 === 材料科學與工程研究所 === 107 === In recent years, the transistors pursue smaller size, lower cost, higher speed and lower power consumption with the era of Internet of Things (IoT), Artificial Intelligence (AI), and Big Data. As devices dimension continuously scale down, the quantity of transistors per unit area was increased, and the total power consumption tends to increase. Thus, the reduction of power consumption becomes an important issue. To reduce the power consumption, negative capacitance (NC) effects can be used for lowering sub-threshold swing (SS) below 60mV/decade of the field effect transistors. With the development of process miniaturization technology, traditional ferroelectric materials such as lead zirconate titanate (PZT) and strontium bismuth tantalite (SBT) are confronted with the problems of scaling difficulty and environmental pollution. Therefore, this study use hafnium aluminum oxide based material as ferroelectric to overcome the problems of device downscaling and environmental pollution. Furthermore, the HfO2-based ferroelectric materials are also well-compatible with recent CMOS process technology. The investigation of ferroelectric hafnium aluminum oxide is helpful for the applications of ferroelectric transistor (FeFET) and ferroelectric memory (FeRAM) integration.
In the previous study, the mechanical stress of the metal gate would induce the crystal phase transformation of the hafnium aluminum oxide material, thereby enhancing the ferroelectric polarization characteristics. In this study, tantalum nitride was used as the metal gate for investigating the effects between material physical properties (such as crystal structure and residual stress) and electrical properties of hafnium aluminum oxide. The experimental results show that the residual stress and sheet resistance are significantly increased when the nitrogen content in tantalum nitride is increased. Since tantalum nitride has a large sheet resistance with high nitrogen content, the polarization current of 9.6 nm hafnium aluminum oxide is suppressed. With thickness scaling of hafnium aluminum oxide film, when the thickness of the hafnium aluminum oxide film is reduced to 7.2 nm, the ferroelectric phase is easily occurred due to lower surface energy. Therefore, compared with 9.6 nm, the 7.2 nm-thick hafnium aluminum oxide will be significantly affected by residual stress of high nitrogen content tantalum nitride, which enhances the generation of polarization current. On the other hand, there is no significant change of residual stress within different thicknesses of tantalum nitride. Therefore, the results show that ferroelectric properties of hafnium aluminum oxide are not affected by thickness effect of tantalum nitride. Besides, the characteristics of the scaled ferroelectric hafnium aluminum oxide film are more susceptible to residual stress of tantalum nitride with different nitrogen content. Compared with the thickness modulation of tantalum nitride, the adjustment of nitrogen content can be used to optimize the metal gate process of the sub-10 nm ferroelectric memory.
|
|---|
